System and method for power-efficient transmission of emg data

ABSTRACT

The system for displaying muscle force data includes a wearable patch and a remote visual display. The wearable patch carries electrodes suitable for sensing electromyographic signals on the skin of the patient. The patch carries circuitry which converts the detected electromyographic signal to a digital output which can be transmitted to the remote visual display. The circuitry relies on filtering to produce a usable digital signal at very low power consumption. The transmitted signal can be used to drive a variety of visual displays, including a conventional hand-held personal communicators and entertainment devices which had been programmed to suitably process the visual display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Application No.61/492,136 (Attorney Docket No. 41569-703.101), filed on Jun. 1, 2011,the full disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to systems and methods formedical monitoring and more particularly to a wireless system forcollecting an electromyogram (EMG) signal and transmitting that signalto a hand-held device, such as a smart cell phone or other personaldigital device having a display.

Neuromuscular feedback can be useful for muscle rehabilitation,relaxation, general conditioning, strengthening, and athletic trainingIn particular, surface electromyography (sEMG) uses skin-mountedelectrodes to collect myoelectric signals associated with thecontraction of a user's muscles. By placing an electrode patch over amuscle or a muscle group which is injured, which is being exercised toincrease strength and/or performance, or which is in a state ofhypercontraction, the activity of that muscle or muscle group can bemonitored quantitatively. For example, a percentage of maximum effortcan be monitored with a visual display provided to the user and/ortrainer in order to optimize a rehabilitation or training protocol.

While such sEMG feedback offers great promise in both rehabilitation andtraining regimens, most sEMG equipment is relatively large, notportable, inconvenient to use, offers limited types of data, andrequires significant energy consumption. It would thus be desirable toprovide low energy consumption systems which are more convenient for theuser and which minimally interfere with the training or other exerciseor muscle control protocols. In particular, it would be desirable toprovide monitoring systems employing an electrode patch which does notneed to be wired to a remote unit for either powering or datacollection. At least some of these objectives will be met by theinventions described herein.

2. Description of the Background Art

U.S. Pat. No. 5,277,197 describes a wearable exercise training systemwhich monitors a muscle force signal (EMG) and provides feedback to theuser. U.S. Pat. No. 4,811,742 describes a table top system for measuringEMG and stimulating muscle groups in response. U.S. Pat. No. 7,563,234describes a rehabilitation system that exercises a body limb andmeasures EMG. Other patents and publications of interest include U.S.Pat. Nos. 5,722,420; 6,238,338; 6,440,067; 6,643,541; 6,984,208;7,152,470; 7,359,750; 7,369,896; 7,602,301; 7,613,510; 7,628,750;7,878,030; U.S. Publ. Nos. 2007/0021689; 2009/0150113; 2009/0171233;2009/0326406; 2010/0106044; 2010/0137735; 2010/0137749; 2010/0234699;2010/0234714. Commercial EMG systems are available from Noraxon USA,Inc., Scottsdale, Ariz. and Thought Technology Ltd., Quebec, Canada.

SUMMARY OF THE INVENTION

The present invention provides a system for monitoring and displayingmuscle force data to a user. The system comprises a wearable patch orsensor unit which carries a pair of spaced-apart sensing electrodes anda ground electrode on a surface thereof. The patch is adapted to besecured to a patient's skin over a muscle group to be monitored with theelectrodes in contact with the skin. Usually, the patch will have anadhesive surface for adhering to the skin, but straps, wraps, fittedclothing, tapes, and other conventional skin fasteners or compressionaids could also be used.

The wearable patch or sensing unit will also carry circuitry needed tomonitor a surface electromyogram (sEMG) signal present on the user'sskin above the target muscle group, digitize the monitored (analog)signal, and wirelessly transmit the signal in the form which may bereceived by a remote monitor. Such wireless transmission will typicallyrely on digital transmission and may conveniently be implemented by aWiFi and/or a blue-tooth enabled personal communication or entertainmentdevice having a display screen and capable of being programmed withsoftware which can process the received signal and display the signal ina desired format. For example, the output may be displayed as a bargraph or other conventional data format (progress meter, line graph, piegraph, XY scatter chart, etc.) which provides an easy visual display ofthe effort being put forth by the user, typically as a percentage ofmaximum effort. Alternatively, the display device may be a dedicatedhand-held, table mounted of other display unit intended for useprimarily or only the patch device of the present invention.

Of particular interest to the present invention, the circuitry on thepatch will be adapted to limit the power required to receive, digitize,process, and transmit the EMG signal to the remote display unit. Thecircuitry will typically include a limited bandwidth amplifier whichreceives signals from the electrodes and produces an analog output. Ananalog-to-digital converter receives and rectifies the analog output ata sample rate in the range from 3000 sec⁻¹ to 4000 sec⁻¹. The patch alsocarries a microprocessor which filters the digital signal from theconverter to produce a smoothed output. In addition, a transmitter isprovided on the patch which receives the output from the microprocessorand generates a wireless signal which can be transmitted to the displayunit.

In particular aspects of the present invention, the sensing electrodesand/or ground electrode on the patch may be coated with silver chloride.The display unit may comprise a hand-held unit, such as a personalcommunicator or entertainment unit, for example an iPhone®, an iPad®, aniPod® Touch®, a Blackberry® phone, an Android® phone, or the like. Thesystem of the present invention, however, is also compatible with laptopcomputers, desktop computers, and other conventional processors withdisplay units having blue-tooth, WiFi, or other wireless receptioncapabilities. Still further, the display could be wall mounted, desktopmounted, or placeable anywhere it is accessible by the user, thephysician, and or the patient.

In a further aspect of the present invention, a method for displayingmuscle force data to a user comprises placing a patch on the user's skinover a muscle group to be monitored. The patch carries electrodes whichengage the skin in order to sense EMG activity and produce a very lowpower analog electrical signal. The very low power electrical signalsensed by the electrodes is filtered and amplified with a limitedbandwidth amplifier disposed on the patch. The filtered and amplifiedsignal, in turn, is converted and rectified to produce a digital signal,where the conversion is at a rate in the range from 3000 sec⁻¹ to 4000sec⁻¹. The digital signal is further filtered by a microprocessor on thepatch to produce a smoothed output. The smoothed output is transmittedto a remote display unit (as described above) which receives anddisplays the smoothed output as a visual representation of the muscleactivity being generated.

It has been found by the inventors herein that the sample rate from 3000sec⁻¹ to 4000 sec⁻¹ provides sufficient samples to digitally filter the400 Hz bandwidth after it is digitally rectified while still achievingrejection of most aliased artifacts. The numerical filter within themicroprocessor then takes the rectified “spiked” signal and produces asmoothed, average signal using digital filtering set up from 0.5 Hz to 3Hz. This approach both sums the data and averages the data to minimizethe traffic and noise in the data collection and presentation. Thesignal may be resampled at 20 sec⁻¹ to capture muscle contractions sothat as much data as possible can be delivered to the device andobserved by the user with minimum energy consumption from the patchbattery. It is important to note that not all raw data is delivered tothe remote visual display. By appropriately filtering the data, onlydata necessary to provide a useful visual presentation of the muscleactivity is provided. The system allows for the delivery of the filteredaverage of the raw data as “data packets” of 20 sec⁻¹ to the remotedisplay device. By thus mathematically offsetting and suppressingunneeded data, a running cumulative average may be provided which issufficient for the user while minimizing the energy consumption of thepatch. Moreover, the integration of the filter, analog-to-digitalconverter, and the microprocessor allows for a further reduction inenergy consumption.

Additionally, session data may be stored and evaluated separately forindication of muscle activity variance that may indicate risk of musclefatigue. Data may be monitored for such deviations by comparison ofsampled data over time to muscle calibration data. As muscle activityslopes downward in effectiveness over time, thresholds that correspondwith muscle fatigue may be established. Once the threshold is reached,data may be delivered to the device and observed by the user to alertthe user to potential for fatigue and a query for reduction or cessationof activity.

In use, the patch and system comprising the patch and a display unitallow muscle activity to be measured and filtered to provide useful datato users. In particular, the useful data comprises information on (1)which muscle is contracting, (2) when the target muscle is contracting,(3) how efficiently the target muscle is contracting, (4) indications orsigns of muscle fatigue, (5) optionally providing a prompt or alert whenthe muscle may be worked harder to achieve a pre-determined goal, (6)optionally providing a prompt or alert when the muscle should be workedless to avoid injury or avoid exceeding a predetermined work pattern,and (7) prompt or alert when the user should relax and, as appropriate,recontract the muscle.

In other aspects of the present invention, the display unit may be usedto adjust the filter bandwidth in the patch circuitry. For example, thebandwidth could be changed to increase or decrease the sensitivity orsmoothness of the data output. Stroke and other patients with very lowmuscle activity would be able to decrease the filtering and increasesensitivity so that they can observe such low activity. Similarly,temperomandibular joint (TMJ) patients can adjust the sensitivity andfiltering to be able to detect release of muscles surrounding the TMJ.

In yet other aspects of the present invention, the patch circuitry couldbe changed to transmit two data streams with the same and/or differentlevels of filtering, e.g., one with high frequency filtering and onewith low frequency filtering. Transmitting two signals with the samefiltering could service different electrode sensors on the patch Thedata streams could be sent selectively, simultaneously, or sequentiallyto the display. The ratio between the high frequency and low frequencyfiltered muscle activity signals can be an indicator of muscle fatigue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary embodiment of a wearable patch placed ona user's quadriceps, constructed in accordance with the principles ofthe present invention. It should be noted that the patch may also beplaced on a variety of other muscles and muscle groups which might bemonitored.

FIGS. 2 and 2A illustrate a system according to the present inventioncomprising a wearable patch and a display unit in the form of a personalcommunication device.

FIGS. 3 through 7 illustrate circuitry which may be employed on thepatch for collecting, filtering, and processing data according to thepresent invention.

FIG. 8 illustrates a communication protocol for storing and sharinginformation acquired by the patch.

DETAILED DESCRIPTION OF THE INVENTION

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

As illustrated in FIG. 1, a patch 10 according to the present inventionwill typically comprise a backing 12, a first sensing electrode 14, asecond sensing electrode 16, and a ground electrode 18. The patch mayoptionally include further sensing and/or ground electrodes, but usuallythe pattern of three electrodes as illustrated will be sufficient. Thepatch 10 will also carry circuitry 19 to receive voltage from theelectrodes 12, 14, convert the voltage to a digital signal, process thedigital signal, and deliver the processed signal to a display unit 20 asdescribed in detail below.

Referring now to FIG. 2, the patch 10 of the present invention will beworn on a user's skin over a target muscle or muscle group which isdesired to be monitored. The patch 10 may be placed over any musclegroup, e.g., as illustrated in the patient's upper leg. Patch 10 may besecured using adhesive placed on the same surface which carries theelectrodes. Alternatively, straps, bandages, or other attachmentmechanisms or devices could be utilized for holding the patch 10 inplace. The system of the present invention will usually include at leasta video display unit 20, typically a hand-held personal communication orentertainment unit of the type described above, and may include audiooutputs as well. Alternatively, the display unit could provide just analphanumeric output, but generally will be desirable to provide a visualdisplay capable of presenting graphic as well as alphanumericinformation to the user.

The system architecture can be understood with reference to FIG. 2A. Thepatch (sEMG device) includes the electrodes (sensors), circuitry toprocess the signal and data, and a wireless transceiver to communicatewith a display (host device). The display also includes a wirelesstransceiver to communicate with the patch. In addition, the displayincludes memory, a user interface UI, a processing unit API, a filemanagement system, and optionally a second transceiver for communicatingwith other units and/or the internet.

Detailed circuitry which may be used to implement the system and methodsof the present invention is provided in FIGS. 3 through 7. The circuitrywill provide the following operative components. A power supplytypically includes a single-cell battery with a voltage from 0.9 V to1.5 V in order to power the patch. The battery voltage is applied to aswitch up converter (U1) to convert the battery voltage to a regulated3.3 V supply for the electronics. This switching converter uses avariable width modulation to alternatively charge inductor L1 withcurrent from the battery and then discharge the inductor through aninternal diode to the energy storage capacitors C2 and C10. The pulsewidth is varied to maintain a constant voltage across these capacitors.The circuitry will typically also include a power switch, a power lightor other indicator, a signal strength indicator, and a battery chargeindicator.

A blue-tooth module U2 controls radio frequency (RF) communication withthe remote display unit. Although blue tooth is shown, virtually anyother low power wireless transceiver or wired connector could be used,e.g., USB, WiFi, ultrawide band, Z-wave, ANT, etc. The module U2establishes a virtual serial connection that has bi-directional,asynchronous port RXD and TXD. Two signals, CTS and RTS, control theflow of data. A virtual link can be established either to a standardcomputer blue-tooth module or to a more specific communications bridge,such as those included in Apple® devices such as the iPhone® and thelike. The blue-tooth module U2 manages communication with an Apple®specific security chip U11 that provides authentication whencommunicating with an Apple® product. Once the virtual link isestablished, further communication with the patch remains the same.

An Atmel® microprocessor U9 controls the acquisition and processing ofdata from the analog signal front end and responds to and sends dataover the virtual link as required. The microprocessor is clocked at3.6864 MHz to allow for exact division to 115 K Baud for serialcommunication. The microprocessor software is stored on an internalflash memory that is loaded with programming hardware from Atmel®. Othermicroprocessors could also be used.

A reference voltage VR is exactly half the 3.3 V power supply. Voltagedivider R4 R5 creates a voltage that is buffered by U4A to provide a lowimpedance source that is connected to the patient through a referenceelectrode TP5. This same voltage provides a reference to thedigital-to-analog converter DAC, U6. U4C is not used.

The electrode signal into the circuitry is applied differentiallybetween TP3 and TP4. An instrumentation amplifier U3 amplifies theelectrode signal and generates an output referenced to VR. Thedifferential amplifier is combined with input capacitors C12 and C13,and an integrator formed by U4B, C17 and R11 works together to form athird order high pass active filter with a corner frequency of about 10Hz. This signal is then applied to amplifier U4D that is configured as athird order, active low pass filter with a corner frequency of about 400Hz that serves as an anti-alias filter for the system. Passivecomponents R8, R9, C18, C15, R10 and C16 are part of this filter. Thefiltered analog signal is then applied to the digital-to-analogconverter U6. Since the DC gain is one, the input to thedigital-to-analog converter is also referenced to VR.

The digital-to-analog converter converts the voltage applied to itsinput pin 2 to a 13-bit result. If its input voltage is equal to VR, theoutput code generated is 0×1000 in HEX. One count lower is O×OFFF andone count higher is 0×1001. The input is sampled when the controlsignal/Cs is brought low and the converted data is clocked out by DCIkon the serial output DOUT. Since the numerical processing in U9rectifies the differential encoded signal, the frequency is effectivelydoubled so that the 400 Hz input signal is handled as if were an 800 Hzsignal. Thus, the sample frequency is set as 4000 sec⁻¹ to reduce themagnitude of alias frequencies to a reasonable level. Note that R17 andR18 are included to prevent the digital-to-analog converter frominterfering with the microprocessor programming when the Pod isconnected to the Atmel® programmer.

Further signal processing is performed by the microprocessor to convertthe 400 Hz differential input into an average amplitude signal with 4degrees of time response. This filtered signal is then sub-sampled at 20sec⁻¹ and sent to the remote display for further interpretation anddisplay.

Referring now to FIG. 8, protocols for storing and transmitting datacollected by the patch are shown:

1. The sEMG device (patch) measures a 0.0−0.2 mV signal from muscle ofthe patient through a skin mounted sensor.

2. The sEMG device (patch) transmits a converted, amplified, rectifiedand filtered signal wirelessly or via a hard wired connection to a hostdevice.

3. The host device (display) displays the real time and historicalsignal to the user in selectable graphical formats. The host stores theresults locally.

4. The host device can transmit stored results using any combination ofwireless or wired connectivity supported by the device encrypted overthe internet.

5. A cloud-based server receives the results and stores the data in aSQL database.

6. Another cloud based component runs a web server.

7. The web server can be accessed via any HTML enabled device.

8. Patients and third parties can compare and/or display historicalinformation.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

1. A system for displaying muscle force data to a user, said systemcomprising: a wearable patch having a pair of spaced-apart sensingelectrodes and a ground electrode on a surface thereof, said patchadapted to be secured to a patient's skin over a muscle group to bemonitored with the electrodes in contact with the skin; circuitry on thepatch including: (a) a limited bandwidth amplifier which receivessignals from the electrodes and produces an analog output; (b) an analogto digital converter that rectifies the signal and samples at a rate inthe range from 3000 sec⁻¹ to 4000 sec⁻¹; (c) a microprocessor whichfilters the digital signal from the converter to produce a smoothedoutput; (d) a transmitter which receives the digital output from themicroprocessor and produces a wireless signal; and (e) a display unitwhich receives the wireless signal from the patch transmitter andproduces a display showing muscle output.
 2. A system as in claim 1,wherein the electrodes are coated with silver chloride.
 3. A system asin claim 1, wherein the surface of the patch is covered with anadhesive.
 4. A system as in claim 1, wherein the display unit comprisesa hand-held unit.
 5. A system as in claim 4, wherein the hand-held unitis a personal communication or entertainment unit having a wirelessreceiver.
 6. A wearable patch for detecting muscle force of a user, saidpatch comprising: a support backing having a pair of spaced-apartsensing electrodes and a ground electrode on a surface thereof, saidpatch adapted to be secured to a patient's skin over a muscle group tobe monitored with the electrodes in contact with the skin; circuitry onthe patch including: (a) a limited bandwidth amplifier which receivessignals from the electrodes and produces an analog output; (b) an analogto digital converter that rectifies the signal and samples at a rate inthe range from 3000 sec⁻¹ to 4000 sec⁻¹; (c) a microprocessor whichfilters the digital signal from the converter to produce a smoothedoutput; and (d) a transmitter which receives the output from themicroprocessor and produces; a wireless signal.
 7. A wearable patch asin claim 6, wherein the electrodes are coated with silver chloride.
 8. Awearable patch as in claim 6, wherein the surface of the support backingis covered with an adhesive.
 9. A method for displaying muscle forcedata to a user, said method comprising: placing a patch on the user'sskin over a muscle group to be monitored, wherein electrodes on thepatch engage the skin, wherein the electrodes sense electromyographic(EMG) activity and produce an analog electrical signal; filtering andamplifying the analog electrical signal with a limited bandwidthamplifier on the patch; converting and rectifying the filtered andamplified analog signal at a rate in the range from 3000 sec⁻¹ to 4000sec⁻¹ to produce a digital signal; filtering the digital signal in amicroprocessor on the patch to produce a smoothed output; transmittingthe smoothed output; receiving and displaying the smoothed output on aremote display unit.
 10. A method as in claim 9, wherein the smoothedoutput is displayed on a remote video and/or audio unit.
 11. A method asin claim 10, wherein the display unit is hand-held.